Detonator

ABSTRACT

In the detonator disclosed, a semiconductor device has its path of major current flow placed in series with a switched power source and a checking apparatus. An explosive adjacent the semiconductor device is set off when the semiconductor device is biased on so it overheats enough to burn out. A checking switch and circuit means test the transistor by biasing it into its low or normal operating range. A meter indicates the operating condition of the semiconductor device without requiring an initiating current. The semiconductor device may be a transistor, a diode, a thyristor, etc.

United States Patent 1191 Sato [4 Sept. 10, 1974 [54] DETONATOR 3,269,315 8/1966 Gauld 102/702 A 3,634,758 1/1972 Flagg 73/167 [75] Inventor- Kaluo Toyota Japan 3,758,131 9/1973 Stephenson et a1 .1 102/39 [73] Assignee: Toyota Jidosha Kogyo Kabushiki Kaisha, Toyota-shi, Aichi-ken,

Primary Examiner-Samuel Feinberg Ja Assistant Examiner-C. T. Jordan Attorne ,A em, or FirmToren, McGead and 22 F led: May 9, 1973 Stangery g y [21] Appl. No.: 358,517

[57] ABSTRACT [30] Foreign Application P i it D t In the detonator disclosed, a semiconductor device May 10 1972 Japan 47-45361 has its Path of major current flow Placed in series with a switched power source and a checking apparatus. [52] CL 102/70 2 A 73/167 102/702 R An explosive adjacent the semiconductor device is set 51 1111.01. F42 11/00 Off when the semiconductor device is biased it [58] Field of Search 102/702 R 70.2 A overheats enough to burn out. A checking switch and 180/82. 280/150 324/158 circuit means test the transistor by biasing it into its low or normal operating range. A meter indicates the [56] References Cited operating condition of the semiconductor device without requiring an initiating current. The semiconductor UNITED STATES PATENTS device may be a transistor, a diode, a thyristor, etc. 2,976,485 3/1961 Bartz 102/702 R 3,211,096 10/1965 Forney et a1 102/702 A 7 Chums, 6 Drawmg Flgures F D 0 IO 24 2 5 26 23 ALARM CKT 29 F LIP- E FLOP PATENTEB SEP 1 01974 ALARM 7 5 CKT FUP- FLOP DETONATOR REFERENCE TO COPENDING APPLICATION This invention is related to the subject matter disclosed in the copending application, Ser. No. 237,362 filed Mar. 23, I972, now US. Pat. No; 3,794,997, and assigned to the same assignee as this application.

BACKGROUND OF THE INVENTION This invention relates to detonators for setting off explosions. The invention has particular relevance to, but is not limited to, detonators for producing explosions which inflate safety air bag devices which have been proposed for automobiles to protect drivers during collisions.

Instantaneous blasting caps which have hitherto been generally employed as detonators use an initiation charge such as a trinitro -resolution, and utilize fine platinum, tungsten, or similar wires for carrying an initiating current. The Joules heat generated in the fine metallic wires upon application of an electric voltage explodes the initiating charge. A number of variables, such as the structure of the detonator, the desired detonating time, the power source to be used, and the reliability of performance intended, limit the resistance of such a wire to several ohms or less. Thus, conventional blasting caps are detonated with the heat of several millijoules. The current that can be permitted to flow through the detonator circuit for checking it is as little as several milliamperes. When the electric wiring is extensive or involves any great contact resistance, detection of a broken wire or circuit discontinuity is simple. However, a short circuit is difficult to find. Thus, it is extremely difficult to obtain reliable performance, with existing mechanism, in applications where a detonator must be checked occasionally after it has been con nected for a long time. For example, it is extremely difficult to test the detonator of the mechanism for actuating an air bag device that protects automobile drivers at the time of a collision.

An object of the present invention is to improve such detonators.

Another object of the invention is to eliminate the beforementioned shortcomings.

SUMMARY OF THE INVENTION According to a feature of the invention, an explosion in a detonator is set off by electrically subjecting a semiconductor element in the vicinity of an explosive to a burnout current.

According to another feature of the invention, the semiconductor device is checked by biasing it into a moderate or high resistance range and detonating it by biasing it into a low resistance range.

According to another feature of the invention, the semiconductor device is in the form of a transistor.

According to another feature of the invention, the semiconductor device is in the form of a diode.

In effect, the invention utilizes a semiconductor device as part of the detonated structure itself, but takes advantage of its ability to be biased into various resistive ranges.

These and other features of the invention are pointed out in the claims forming a part of this specification. Other objects and advantages of the invention will become evident from the following detailed description when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic cross-sectional view illustrating a transistorized blasting cap.

FIG. 2 is a schematic circuit diagram of a detonator system using the transistorized blasting cap of FIG. 1 and circuit means for detecting any defects or anomalies, which defects are indicated by a voltmeter.

FIG. 3 is a schematic circuit diagram of a detonator system using the transistorized blasting cap of FIG. 1 and using an alarm to indicate defects. I

FIG. 4 is a schematic view illustrating the construction of a diode-actuated blasting cap.

FIG. 5 is an electric circuit diagram of a detonator using the diode-actuated blasting cap of FIG. 4; and

FIG. 6 is a schematic illustration of a vehicle utilizing the detonator of FIGS. 1 to 5.

DESCRIPTION OF PREFERRED EMBODIMENTS IN FIG. 1, a mesa transistor 1 initiates explosion of a blasting cap BC. In the transistor 1, a P-type germanium region forms a base and carries a base electrode 2. Two N-type germanium regions of the transistor form a collector and an emitter, respectively, and: carry a collector contact or electrode 3 and an emitter contact or electrode 4. A base plate 5 on which the initiating transistor 1 is fixedly mounted, carries pins connected to lead wires 6 which connect the respective collector electrode 3 and emitter electrode 4 to their respective transistor regions.

An explosive charge 7 is mounted close to the transistor 1. The transistor 1 and the explosive 7 is protected by the plate 5 and a cover 8 of thin sheet metal which can be readily broken by an explosion. Usually a transistor develops very little heat in its semiconductive portions when it is nearly non-conductive because of negligible base current. However, an increase in base current produces a temperature rise. For example, when the voltage between the collector and the emitter is 10 volts and the base current is 1 mA, the transistor is rendered conductive. If a collector current of about mA flows therethrough, the transistor will develop more than one Joule of heat per second and will burn out at once. To avoid this, a heat sink is usually formed adjacent either the collector or the emitter in order to dissipate the heat. A generous allowable heat loss is provided for the collector.

In FIG. 1, the initiating transistor 1 is made sufficiently conductive so that a collector-to-emitter current flows which is in excess of the allowable loss and sufficient to burn out the transistor. The current is made sufficiently great so that the Joule heat generated in the transistor 1 can set off the explosive 7 to produce detonation. Prior to detonation the initiating transistor is made nearly non-conductive with negligible base current. When the transistor 1 is made non-conductive, the collector current is reduced almost to zero. In this way the circuit and the associated components can be checked.

FIG. 2 illustrates a circuit diagram in which the transistor l is connected for detonation of the blasting cap in FIG. 1. In FIG. 2, the emitter of the initiating transistor l is connected to the collector of a checking or test transistor 10 having a greater allowable collector current than the transistor 1. The bases of both transistors l and receive current through the ganged armatures 12 and 13 of a double-pole triple-throw switch 11. Fixed portions 14 and 15 of the switch 11 each have three contacts a, b, and c. The armatures l2 and 13 contact the contacts have the same designation simultaneously. Thus, the switch 11 has an intiating position a, a stand-by position b, and a check position 0, (i.e. a test position).

The contacts a and c of the portion 14 which serve the initiating transistor 1, are connected directly to the positive terminal of a power source 16. The contact b of portion 14 is connected to the same terminal through a high resistance 17. The contacts a, b, and c of the portion 15, which serve the checking transistor 10, are all connected to the positive terminal of the power source 16 through a resistor 18 exhibiting a low resistance. However, a high resistance resistor 19 intervenes between the contacts c and the resistor 18.

The collector of the initiating transistor 1 receives its current directly from the positive terminal of the power source 16. The emitter of the checking transistor is connected directly to the negative terminal of the power source. The collector of the transistor 10 and the emitter of the transistor 1 are connected to each other. A voltmeter 20, connected between the emitter and collector of transistor 10 indicates the result of an operational check. When the armatures or movable contacts 12 and 13 of the switch 11 are in the standby positions, that is when they contact the contacts b of the portions 14 and 15, the initiating transistor is nearly non-conductive. The base current is reduced to a negligible value by the high resistance of resistor 17. Thus, no detonation takes place. On the other hand, checking transistor 10 receives an intense base current through the low resistance of resistor 18 and is rendered sufficiently conductive to result in a saturation current. As a result, the resistance between its collector and emitter is reduced almost to zero. Thus, as long as there is not defect between the collector and the emitter of the initiating transistor 1 and in the circuit connected thereto, the reading of the voltmeter 20 remains substantially zero. However, if there is a short-circuit, the voltmeter reading will correspond to the voltage of the source 16.

Shifting of the switch 11 to the check or test position c, that is the position in which the armatures or movable contacts 12 and 13 contact the contacts 0 of portions 14 and 15, causes an increase in the base-emitter current through the transistor 1. This biases the transistor 1 toward heavy conduction. At the same time, however, the base current to the transistor 10 is reduced by the high resistance of resistor 19. Thus, the checking transistor becomes nearly non-conductive. This produces a substantial increase in the resistance between its collector and emitter. Thus, as long as the circuitry is normal and sound, the reading of the voltmeter 20 is about equal to the source voltage. In case of a defect such as a broken wire or circuit discontinuity, the source voltage is not indicated. In the latter case, notwithstanding the potentially conductive state of the initiating transistor, the virtual non-conductivity of the checking transistor makes it impossible for current to flow through the initiating transistor with sufficient intensity to cause a detonation.

Shifting the switch 11 to the initiating position a where the armatures 12 and 13 contact the contacts a,

renders both transistors 1 and 10 conductive. This permits the flow of high collector current through the initiating transistor 1. It results in the development of sufficient heat to induce detonation. Any defect in the circuitry can be detected from the readings of the voltmeter 20 in the positions 12 and c of the switch 11. According to other embodiments of the invention, the transistor action is realized with other elements such as thyristors.

FIG. 3 illustrates another embodiment of the invention. Here, the collector of the checking transistor 10 again connects to the emitter of the initiating transistor 1. The collector of the transistor 1 is in turn connected to a terminal A of a power source similar to the embodiment of FIG. 2. The arrangement is such that when both transistors l and 10 are non-conductive, the leakage current of the transistor 1 exceeds that of the transistor 10.

The base of the initiating transistor 1 receives current from the output side of an AND circuit 21. The AND CIRCUIT 21 receives one input from an initiatingsignal input terminal B. A checking or test signal input terminal D applies a voltage to the base of the checking transistor 10 through a NOT circuit 23. A point F connecting the two transistors 1 and 10, and a terminal D both supply the input to a nonharmonic circuit or EX- CLUSIVE OR gate 24.

The output of the nonharmonic circuit 24 is connected to an alarm circuit 26 through an OR gate 25. Together with the terminal D, EXCLUSIVE OR gate 24 controls another input terminal of the OR gate 25 through the setting side of a flip flop circuit 28. The circuit 24 further connects to the inverter input of AND gate 21. The outputs of the NOT gate 23 and an AND gate 27 are connected to a normal-signal output terminal E through a NOR gate 29. A reset terminal G resets the flip flop 28.

During standby, when no input signal is applied to terminal D, the output of the NOT gate 23 is one or high and the checking transistor is conductive. Thus, when the initiating transistor is non-conductive and the signal at the point F is zero and with no defect in the circuit, the output of the EXCLUSIVE OR gate 24 becomes zero because both inputs are zero. The output of the AND gate 27 also becomes zero because both the inputs are zero. Thus, the OR gate 25 yields no output and produces no alarm. At this point both inputs of the NOR gate 29 are one and zero. Therefore, the output of the NOR gate 29 becomes zero. The zero output signal from the nonharmonic circuit 24, applied to the inverting input of the gate 21, enables the gate 21.

When a signal is applied to the terminal D to produce a checking condition, the output of the NOT circuit'23 becomes zero and renders the checking transistor 10 non-conductive. If there is no defect in the circuit, and the initiating transistor 1 is also rendered nonconductive, the differences between the current leakages of the two transistors 1 and 10 changes the signal at the point F to one. The output of the EXCLUSIVE OR circuit 24 remains zero because both inputs are one. The output of the AND gate 27 remains zero because the inputs thereto are zero and one. As a result, no alarm is sounded. At this point both inputs of the NOR gate 29 are zero. Therefore, an output signal one passes to the terminal E.

The following defects can be expected in the circuit of FIG. 3:

Signal Signal Defect Position Warning Detonation at D at F stand-by 0 1 ON I impossible checking l I stand-by 0 0 II impossible checking I 0 ON stand-by 0 I ON III impossible checking l l stand-by 0 0 IV impossible checking l 0 ON The output one of the terminal E can be used for checking when a special electronic circuit is additionally provided for checking. When the output one appears at the terminal E, the initiating-signal input terminal B, although supplied with the signal one, does not cause detonation. Namely, when a signal is applied to the terminal D and the output of the EXCLUSIVE OR gate 24 becomes zero, an output signal one passes to the terminal E. At this time, the output of the NDT circuit 23 becomes zero and renders the checking resistor non-conductive. Therefore, the initiating signal input terminal B, although supplied with the signal one, does not cause detonation. Therefore, it is possible to apply a check signal one, which may be generated periodically by an electronic timer or the like, to the checksignal input terminal D and at the same time to apply a signal one to the initiating-signal input terminal B only when the circuit is sound, that is, when the signal one appears at the terminal E. Thus the whole circuit including the lead from the terminal B to the inhibit gate may be checked.

For manual checking the terminal E is directly connected to the terminal B.

FIG. 4 shows a cross-section of a diode-actuated blasting cap which represents another embodiment of the invention. P-type and N-type germanium regions form a PN junction diode 30 for initiation. An anode 31 and a cathode 32 connect the germanium regions to wires 33. An explosive 34 is mounted close to the lead wires 33 near the respective electrodes, i.e. the anode and cathode, 31 and 32. A case 35 surrounds the assembly.

The open end of the case 35 is covered by a sheet 36 that can readily be broken upon detonation.

Generally, a diode has a very great reverse resistance. The heat generated in the semiconductor junction by a forward current is dissipated, generally, by a heat sink or heat sinks adjacent the anode and cathode. This embodiment of the invention takes advantage of the high reverse resistance for checking purposes. Heating of the diode 30 by the large forward current causes explosion of the explosive 34.

FIG. 5 is a circuit diagram utilizing the diode of FIG. 4. Here, a resistor 37 having a high resistance provides a high resistance path from the anode of the diode 30 to ground. A voltmeter 38 measures the voltage of the anode of the diode 30 relative to ground. An initiating switch 39 connects the anode of the diode 30 to the positive terminal of a power source 40 whose negative terminal is grounded. A checking switch 41, when placed in position a, allows a power source 42 to apply an inverse biasing voltage to the cathode of the diode 30. In the position b the switch 41 grounds the cathode.

In operation, when the initating switch 39 of FIG. 5 is off, and the checking switch 41 is set at position a for testing the apparatus, the source 42 inversely biases the diode 30 through the resistor 37. When the circuit and the associated components operate normally, a small current flows in the reverse direction. The high resistance of resistor 37 causes the voltmeter 38 to exhibit a relatively high value. However, a reading of the voltmeter 38 would be less than the value of the voltage of the source 42.

If the diode 30 were short-circuited, the reading of the voltmeter 38 would equal the voltage of the power source 42. If there were any discontinuity in the circuit, the reading would drop to zero. When the switch 41 is set to the position b and the initiating switch 39 is closed to produce detonation, the voltage of the power source is applied in the forward direction across the initiating diode 30. A high, intense short-circuiting current flows through the diode to induce an explosion.

According to another embodiment of the invention, the source 42 is connected in a direction reverse to that direction shown in FIG. 5. The values of the source 42 and the resistor 37 are such as to produce a slight forward current, too small to produce detonation, through the diode 30 and the resistor 37.

The resulting barrier voltage of about 0.6 volts for a silicon diode at the PN junction permits an operator to check for defects or anomalies in the circuit or diode According to the present invention, as shown by the above described embodiment, it is possible to set off an explosive 7 or 34 with a transistor 1 or a diode 30 to detonate an explosion. The characteristics of either the transistor or diodes semi-conductor element make it possible to check the element and its circuitry with a current far more intense and measurable than can be accomplished with an ordinary fine metallic wire. Thus, the invention affords the possibility of accurate testing with greater reliability than heretofor. The advantage is beneficially applicable to the actuating mechanisms of air bag devices.

According to another embodiment of the invention, the circuits in FIGS. 2 and 3 using the blasting cap of FIG. 1, and the ciruit of FIG. 5 using the blasting cap of FIG. 4 form part of a safety device in an automobile. This is illustrated in FIG. 6 wherein a safety control system SCS provides an initiating signal to a detonator DET to inflate an air bag AB in a vehicle VE. The detonator DET is composed of the circuit of FIG. 2 or 3 which includes the blasting cap of FIG. I, or the circuit of FIG. 5 including the blasting cap of FIG. 4. The safety control system SCS may be of any of the known types which respond to a collision of the vehicle VE or an impending collision. An example of such a system can be found in the copending application Ser. No. 237, 362 filed Mar. 23, 1972, now US. Pat. No. 3,794,997, and assigned to the same Assignee as the present application. An indicator I corresponding to members 30, 28 and 26 forms part of the detonator DET and is mounted on the dashboard of the vehicle.

In FIG. 3, a zero at the output of EXCLUSIVE OR circuit 24 indicates that the terminals D and F are at the same potential and enables the gate 21. This allows an initiating signal at the terminal B to turn on the transistor l to set off an explosive near the transistor 1 in F 1G. 1. A defect causes the terminals D and F to exhibit different values and turn on the alarm circuit 26. It should be noted that in the aforementioned table, the warning appears in the alarm circuit 26.

An output from the circuit 24 which would produce a warning in the alarm circuit 26 and disables the AND gate 21.

It should be noted that the heat in the semiconductor also conductively heats the connecting wires which help set off the explosive.

While embodiments of the invention have been described in detail, it will be obvious to those skilled in the art that the invention may be embodied otherwise without departing from its spirit and scope.

What is claimed is:

1. A detonator, comprising an explosive, a semiconductor element near enough to the explosive so that the explosive can be set off by heat from the semiconductor element, circuit means for passing a current through said semiconductor element, said circuit means having initiation means for setting the current passed through the element to a value sufficient to heat the element enough to set off the explosive, said circuit means having test means for regulating the current through said semiconductor elements to a value less than sufficient to heat the element enough to set off the explosive, indicating means in said circuit means encoupled to said semiconductor element for indicating a value indicative of current through said semiconductor element.

2. A detonator as in claim 1, wherein said semiconductor element includes a transistor having a path of major current flow, said initiating means including potential application means for biasing the transistor into a state of high current conduction along the path of major current flow sufficient to heat the transistor, said test means including potential application means for biasing the transistor into a condition in which the current flow through the path of major current flow is insufficient to heat the transistor enough to set off the explosive, said indicating means including a meter measuring the effect of current flow through said transistor.

3. A detonator as in claim 1, wherein said semiconductor element is a diode, wherein said initiating means includes a circuit for applying forward current through the diode sufficient to heat the diode enough to set off the explosive, said test means including a circuit for passing a reverse current through the diode insufficient to heat the diode to a level enough to set off the explosive.

4. A detonator as in claim 2, wherein said test means including a second transistor having a path of major current flow in series with the path of major current flow of said first transistor, said indicating means being connected across the path of major current flow of said second transistor, said initiating means including biasing means for biasing said second transistor into heavy conduction when said initiating means biases said first transistor into heavy conduction, said test means including second biasing means for biasing said second transistor into heavy conduction when said initiating means biases said first transistor into conduction insufficient to set off the explosive, said circuit means including third biasing means for biasing said second transistor into a state of limited conduction and for biasing said first transistor into heavy conduction.

5. A detonator comprising a blasting cap including an explosion-initiating transistor having a collector and an emitter and a base, lead wires connected to the collector and emitter and base, said blasting cap having an explosive disposed close to the lead wires connected to the collector and emitter of the transistor, a checking transistor having a collector and an emitter and a base, a voltmeter, a power source, a switch, said transistors having respective paths of major current flow between said emitters and said collectors, said checking transistor being connected so that its path of major current flow is in series with the path of major current flow of the initiating transistor for checking current through the initiating transistor, a voltmeter connector to indicate the current through the initiating transistor, said transistors being connected at their base to said power source through said switch to vary the base current so that when both transistors are made conductive an explosion is set off and when either transistor is made conductive said voltmeter indicates predetermined readings in the absence of affects and other readings in the presence of defects.

6. A detonator, comprising an explosive, an explosion-initiating transistor forming a path of major current flow and having an emitter and a collector, lead wires connected to the emitter and collector, a checking transistor having an emitter and collector and forming a path of major current flow in series with the path of major current flow of the initiating transistor, said initiating transistor having a base, an AND gate having an output connected to the base of the initiating transistor, and input terminal for an explosion-initiating signal, said input terminal being connected to an input of said AND gate, a NOT gate, said checking transistor having a base, a check terminal for forming an input for a checking signal, said NOT circuit connecting the base of said checking transistor to said check terminal, said transistors forming a common point along their paths of major current flow, an EXCLUSIVE OR gate connected and responsive to the check terminal and the common point, an alarm circuit connected to the output of said EXCLUSIVE OR gate and an inhibitor circuit having an input coupled to the output of said EX- CLUSIVE OR gate and connected to an input of said AND gate, said initiating transistor when biased fully on together with said checking transistor being biased fully on producing sufficient heat to set off said explosive, said transistors having characteristics so that when one is biased on and the other is biased off the EXCLU- SIVE OR gate compares the voltage at the common point with the check input to set off said alarm circuit.

7. A detonator, comprising a semiconductor blasting cap having an explosion-initiating diode and an explodiode having a characteristic such that when a sufficient forward current is applied to the diode the diode is heated sufficiently to set off an explosion and when an inverse bias voltage is applied to the diode the current is insufficient to heat the diode and set off the explosion, indicator means connected to said circuit to indicate the degree of current flow through said diode. 

1. A detonator, comprising an explosive, a semiconductor element near enough to the explosive so that the explosive can be set off by heat from the semiconductor element, circuit means for passing a current through said semiconductor element, said circuit means having initiation means for setting the current passed through the element to a value sufficient to heat the element enough to set off the explosive, said circuit means having test means for regulating the current through said semiconductor elements to a value less than sufficient to heat the element enough to set off the explosive, indicating means in said circuit means encoupled to said semiconductor element for indicating a value indicative of current through said semiconductor element.
 2. A detonator as in claim 1, wherein said semiconductor element includes a transistor having a path of major current flow, said initiating means including potential application means for biasing the transistor into a state of high current conduction along the path of major current flow sufficient to heat thE transistor, said test means including potential application means for biasing the transistor into a condition in which the current flow through the path of major current flow is insufficient to heat the transistor enough to set off the explosive, said indicating means including a meter measuring the effect of current flow through said transistor.
 3. A detonator as in claim 1, wherein said semiconductor element is a diode, wherein said initiating means includes a circuit for applying forward current through the diode sufficient to heat the diode enough to set off the explosive, said test means including a circuit for passing a reverse current through the diode insufficient to heat the diode to a level enough to set off the explosive.
 4. A detonator as in claim 2, wherein said test means including a second transistor having a path of major current flow in series with the path of major current flow of said first transistor, said indicating means being connected across the path of major current flow of said second transistor, said initiating means including biasing means for biasing said second transistor into heavy conduction when said initiating means biases said first transistor into heavy conduction, said test means including second biasing means for biasing said second transistor into heavy conduction when said initiating means biases said first transistor into conduction insufficient to set off the explosive, said circuit means including third biasing means for biasing said second transistor into a state of limited conduction and for biasing said first transistor into heavy conduction.
 5. A detonator comprising a blasting cap including an explosion-initiating transistor having a collector and an emitter and a base, lead wires connected to the collector and emitter and base, said blasting cap having an explosive disposed close to the lead wires connected to the collector and emitter of the transistor, a checking transistor having a collector and an emitter and a base, a voltmeter, a power source, a switch, said transistors having respective paths of major current flow between said emitters and said collectors, said checking transistor being connected so that its path of major current flow is in series with the path of major current flow of the initiating transistor for checking current through the initiating transistor, a voltmeter connector to indicate the current through the initiating transistor, said transistors being connected at their base to said power source through said switch to vary the base current so that when both transistors are made conductive an explosion is set off and when either transistor is made conductive said voltmeter indicates predetermined readings in the absence of affects and other readings in the presence of defects.
 6. A detonator, comprising an explosive, an explosion-initiating transistor forming a path of major current flow and having an emitter and a collector, lead wires connected to the emitter and collector, a checking transistor having an emitter and collector and forming a path of major current flow in series with the path of major current flow of the initiating transistor, said initiating transistor having a base, an AND gate having an output connected to the base of the initiating transistor, and input terminal for an explosion-initiating signal, said input terminal being connected to an input of said AND gate, a NOT gate, said checking transistor having a base, a check terminal for forming an input for a checking signal, said NOT circuit connecting the base of said checking transistor to said check terminal, said transistors forming a common point along their paths of major current flow, an EXCLUSIVE OR gate connected and responsive to the check terminal and the common point, an alarm circuit connected to the output of said EXCLUSIVE OR gate and an inhibitor circuit having an input coupled to the output of said EXCLUSIVE OR gate and connected to an input of said AND gate, said initiating transistor wheN biased fully on together with said checking transistor being biased fully on producing sufficient heat to set off said explosive, said transistors having characteristics so that when one is biased on and the other is biased off the EXCLUSIVE OR gate compares the voltage at the common point with the check input to set off said alarm circuit.
 7. A detonator, comprising a semiconductor blasting cap having an explosion-initiating diode and an explosive, said diode having an anode and a cathode and lead wires connected to the anode and the cathode, an explosive in said blasting cap disposed close to said diode, circuit means connected to the initiating diode for furnishing current in the forward direction through said diode, said circuit means including a resistance, a voltmeter, an explosion initiating switch, and switch means for applying an inverse bias voltage, said initiating diode having a characteristic such that when a sufficient forward current is applied to the diode the diode is heated sufficiently to set off an explosion and when an inverse bias voltage is applied to the diode the current is insufficient to heat the diode and set off the explosion, indicator means connected to said circuit to indicate the degree of current flow through said diode. 